Political activist Deji Adeyanju and two others are still in police custody 48 hours after their arrest.
Mr Adeyanju, Daniel Abobama and Boma Williams were part of a demonstration in Abuja on Wednesday morning.
Police spokesperson Jimoh Moshood said they were arrested for criminal defamation and breach of public peace.
Mr Moshood added that the arrest did not violate either the Nigerian Constitution or the police establishment powers and that the trio had already been arraigned in an Abuja court.
Since their arrest, there have been calls for their release including from Amnesty International.
Adeyanju has led regular protests against alleged injustice and other highhanded conducts of public institutions and individuals, frequently clashing with security agencies.
He had been arrested at least three times in 2018, all while leading or participating in protests.
